The Bureau of Mines measured the energy requirements for the spark ignition in air of Pittsburgh seam bituminous coal dust, lycopodium spores, and polyethylene powder with a 1.2-L furnace and 8-l and 20- l chambers. Thermal autoignition temperatures of the same dusts were measured in the 1.2-L furnace. Electrical ignition requirements are given in terms of both effective spark gap energies, eeff, and stored circuit energies, 1/2 ce2. The measured order of electrical ignitability for the three dusts is consistent with the data of other researchers; however, the absolute values are systematically higher, probably because of higher flow and turbulence levels in the chambers used and lower electrical efficiency in the circuit used here. The temperature dependence of the lean limit of flammability for lycopodium was measured with the 1.2-L system, and those measurements confirm the applicability of the modified Burgess-Wheeler Law to a dust. Owing to experimental complexities, the minimum ignition energies for dusts may not reflect intrinsic flammability behavior. However, some valuable information may be obtained from the relative ignition energies of various dusts at ambient and elevated temperatures. In addition, the concept of minimum electrical ignition energies for homogeneous gas mixtures is reevaluated theoretically.